Transmission power control method for a wireless communication system

ABSTRACT

Transmission power relative to a propagation path having a variation in gain is controlled to increase communication channel capacity, and a data rate is controlled in accordance with the variation of the increased communication channel capacity. In order to increase the communication channel capacity, the transmission power is determined so that the sum of noise power (=received noise power/propagation path gain) converted into one at a transmitter and the transmission power becomes constant. As a result, contrary to the background art, the transmission power is controlled to be reduced when the propagation path gain decreases and to be increased when the propagation path gain increases.

The present application is a continuation application of applicationSer. No. 11/812,693, filed Jun. 21, 2007, which is a Divisionalapplication of application Ser. No. 10/287,676, filed Nov. 5, 2002 (nowU.S. Pat. No. 7,428,264), the contents of which are incorporated hereinby reference.

BACKGROUND OF THE INVENTION

The present invention relates to a method for controlling wirelesstransmission power and a communication channel data rate in a wirelesscommunication system, and particularly preferably applied to a mobilecommunication system.

In wireless communication systems, there are known techniques forcontrolling transmission power of a Wireless Communication Station inorder to obtain a desired reception quality. For example, U.S. Pat. No.5,267,262, Qualcomm Inc., “Transmitter Power Control System” discloses atechnique in a CDMA mobile communication system as follows. That is,signal received power from each mobile station is measured in a basestation. When the measured signal received power is lower than a desiredvalue, an instruction to increase transmission power is transmitted tothe mobile station. When the measured signal received power is higherthan the desired value, an instruction to reduce the transmission poweris transmitted to the mobile station. The mobile station controls thetransmission power in accordance with the aforementioned transmissionpower control instruction. Thus, the received power in the base stationis kept substantially constant.

In addition, U.S. Pat. No. 5,559,790, Hitachi Ltd., “Spread SpectrumCommunication System and Transmission Power Control Method therefor”discloses a technique as follows. That is, each mobile station measuresthe reception quality of a pilot signal transmitted with known power bya base station. On the basis of that measuring result, the mobilestation transmits a transmission power control signal to the basestation for requesting higher transmission power in the case where thereception quality is bad than in the case where the reception quality isgood. The base station controls the transmission power of a signal sentto the mobile station, on the basis of the transmission power controlsignal. Thus, the signal reception quality from the base station is keptsubstantially constant in the mobile station.

Each of these techniques is aimed at controlling received power orquality on the reception side to be constant. That is, in a transmissionpower control method using any of the aforementioned background-arttechniques, the reception quality is made constant enough to preventdeterioration of reception quality caused by a gain variation in apropagation path or in-system interference caused by unnecessarilyexcessive transmission power.

However, assume that there is a fading which is a propagation path gainvariation having a comparatively short period of time and generated as amobile station moves. In such a case, when the background-art techniquesare used, the transmission power becomes very high when the propagationpath gain drops down instantaneously. Thus, average transmission powerincreases. The increase of the average transmission power increasesmutual interference provided for the system as a whole, and results inlowering of communication throughput in the system as a whole. Inaddition, in a mobile station, the increase of the average transmissionpower increases power consumption so that the time allowed to talkbecomes short.

SUMMARY OF THE INVENTION

It is therefore a first object of the present invention to provide atransmission power control method for attaining a desired receptionquality while preventing increase in average transmission power evenwhen there occurs a propagation path gain variation having acomparatively short period of time.

In addition, when the average transmission power is not increased,average received power is reduced. The deterioration of the receptionquality (SN ratio or SNR) caused by the reduction results in lowering inthe capacity of the communication channel. That is, the maximum datarate at which communication can be made is lowered. It is therefore asecond object of the present invention to keep the communication channelcapacity as large as possible even when there occurs a propagation pathgain variation having a comparatively short period of time.

In addition, when the communication channel capacity per time varies dueto a variation of the propagation path gain, there is a problem that thetime required for making communication for desired information varies sothat stable communication quality cannot be obtained. It is therefore athird object of the present invention to provide stable communicationquality even when the communication channel capacity per time varies.

Means for solving the foregoing problems has a feature in that means formeasuring a propagation path gain and reception quality and means fortransmitting transmission power control information and receptionquality information are provided in a first Wireless CommunicationStation, and means for receiving the aforementioned transmission powercontrol information and the aforementioned reception quality informationand means for controlling transmission power and a data rate areprovided in a second Wireless Communication Station, while the secondWireless Communication Station includes control means for making controlto increase the transmission power of the second Wireless CommunicationStation when the propagation path gain becomes high, and to reduce thetransmission power of the second Wireless Communication Station when thepropagation path gain becomes low. In addition, the second WirelessCommunication Station includes control means for making control toincrease the data rate when the reception quality is good, and to reducethe data rate when the reception quality is not good. Further, if thetransmission power is reduced when the propagation path gain is low,there may occur dispersion in quality of Received Data or omission inthe Received Data. The dispersion or the omission is remedied bypowerful error correction codes represented by turbo codes.

Other aspects of the present invention will be made clear in thefollowing embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing an example of a time variation of apropagation path gain.

FIG. 2 is a graph showing an example of a time variation of noise power.

FIG. 3 is a graph showing an example of a time variation of equivalentnoise power at a transmitter.

FIG. 4 is a graph showing an embodiment of transmission power controlaccording to the present invention.

FIG. 5 is a graph showing an example of a time variation of receivedpower according to the present invention.

FIG. 6 is a graph showing an example of transmission power controlaccording to the background art.

FIG. 7 is a graph showing an example of a time variation of receivedpower according to the background art.

FIG. 8 is a graph showing comparison of transmission power bytransmission power control according to the present invention with thataccording to the background art.

FIG. 9 is a graph showing a second example of a propagation path gainvariation.

FIGS. 10A-10D are graphs showing a second embodiment of transmissionpower control according to the present invention.

FIG. 11 is a block diagram of an example of configuration of areception-side Wireless Communication Station according to the presentinvention.

FIGS. 12A-12C are format diagrams of first examples of a transmissionsignal multiplexing format in a transmission-side Wireless CommunicationStation according to the present invention.

FIG. 13 is a block diagram showing a configuration of thetransmission-side Wireless Communication Station according to thepresent invention.

FIGS. 14A and 14B are format diagrams of examples of a transmissionsignal multiplexing format in the reception-side Wireless CommunicationStation according to the present invention.

FIG. 15 is a block diagram of a first configuration example of atransmission power control signal generating portion according to thepresent invention.

FIG. 16 is a block diagram of a first configuration example of atransmission power control portion according to the present invention.

FIG. 17 is a block diagram of a second configuration example of anencoder with a data rate control function according to the presentinvention.

FIG. 18 is a block diagram of a second configuration example of adecoder with a data rate control function according to the presentinvention.

FIG. 19 is a block diagram of a second configuration example of atransmission power control signal generating portion according to thepresent invention.

FIG. 20 is a block diagram of a third configuration example of atransmission power control signal generating portion according to thepresent invention.

FIGS. 21A and 21B are format diagrams of second examples of atransmission signal multiplexing format in the transmission-sideWireless Communication Station according to the present invention.

FIG. 22 is a block diagram of a fourth configuration example of atransmission power control signal generating portion according to thepresent invention.

FIG. 23 is a block diagram of a second configuration example of atransmission power control portion according to the present invention.

FIG. 24 is a block diagram of a fifth configuration example of atransmission power control signal generating portion according to thepresent invention.

FIG. 25 is a block diagram of a third configuration example of atransmission power control portion according to the present invention.

FIGS. 26A and 26B are format diagrams of third examples of atransmission signal multiplexing format in the transmission-sideWireless Communication Station according to the present invention.

FIG. 27 is a block diagram of a sixth configuration example of atransmission power control signal generating portion according to thepresent invention.

FIG. 28 is a block diagram of a seventh configuration example of atransmission power control signal generating portion according to thepresent invention.

FIG. 29 is a block diagram of a fourth configuration example of atransmission power control portion according to the present invention.

FIG. 30 is a system configuration diagram according to the presentinvention.

FIG. 31 is a flow chart of an example of a flow of processing of datarate control means according to the present invention.

FIG. 32 is a block diagram of a configuration example of an errorcorrection encoder of a transmission-side Wireless Communication Stationaccording to the present invention.

FIG. 33 is a block diagram of a configuration example of an errorcorrection decoder of a reception-side Wireless Communication Stationaccording to the present invention.

DESCRIPTION OF THE EMBODIMENTS

First, description will be made on a power control algorithm accordingto the present invention.

FIG. 1 is a graph showing an example of a time variation of apropagation path gain. Now, consider that the propagation path gain hasa variation as shown in FIG. 1. That is, consider a propagation path inwhich gains at time instants t1, t2, t3 and t4 are 2, 1, ⅓ and ⅔respectively so that the average gain is 1.

FIG. 2 is a graph showing an example of a time variation of noise power.

FIG. 3 is a graph showing an example of a time variation of equivalentnoise power at a transmitter. Assume that constant noise with power of 1is added on the reception side as shown in FIG. 2. This is equivalent tothe case where noises of powers ½, 1, 3 and 3/2 are added on thetransmission side at the time instants t1, t2, t3 and t4 respectively asshown in FIG. 3. That is, a variation of the propagation path gain canbe regarded as a variation of noise power equivalently.

On the other hand, it is known that capacity C of a communicationchannel is theoretically expressed by C=W log 2(1+S/N). Here, Cdesignates the number of transmissible bits per second, W designates thefrequency band width, S designates the signal power, N designates thenoise power, and log 2(x) designates the logarithm of x to the base of2. Accordingly, the communication channel capacity in a propagation pathvarying with time as described above is expressed by C=Ave(W log2(1+S(t)/N(t))) where S(t) and N(t) designate signal power and noisepower at a time instant t respectively. Here, Ave(x) designates the timeaverage of x. Accordingly, if S(t) is varied with time by power control,the communication channel capacity will vary. In the present invention,the transmission power is controlled to make the communication channelcapacity as large as possible. Specifically, control is made as follows.

Now, consider S(t) that maximizes the communication channel capacity Con the assumption that the average transmission power, that is, the timeaverage Ave(S(t)) of S(t) is constant. Since Ave(S(t)) is constant, iftransmission power at one time instant is increased, transmission powerat another time instant has to be reduced. Here, the increasing rate ofC relative to a very small increase of S is expressed bydC/dS=W/log(2)/(N+S) on the basis of the aforementioned definitionalexpression of the communication channel capacity. Accordingly, whenfixed power is distributed timewise, the communication channel capacitywill be increased to a maximum if the transmission power is distributedto a minimum of N+S. If the transmission power is sequentiallydistributed thus to the minimum of N+S, N+S will be constant finallywhen all the power has been distributed. In addition, S will not bedistributed at all to a period of time in which N is larger than theattained S+N. In such a state, the communication channel capacity willbe largest.

Here, assume that the noise power received by a receiver is expressed bya function Nr(t) of time, and the propagation path gain is expressed bya function g(t) of time. Then, equivalent noise power N(t) viewed on thetransmitter side is expressed by:

N(t)=Nr(t)/g(t)

Accordingly, the aforementioned transmission power S(t) that maximizesthe communication channel capacity satisfies the following condition:

N(t)+S(t)=Nr(t)/g(t)+S(t)=P_const.

-   -   (constant)        That is, it will go well if control is made to satisfy:

S(t)=P_const−Nr(t)/g(t)

Then, the real transmission power is set at 0 (that is, transmission issuspended) when S(t)<0. Incidentally, if P_const is increased, theaverage transmission power and the communication channel capacity willincrease. On the contrary, if P_const is reduced, the averagetransmission power and the communication channel capacity will decrease.Accordingly, it will go well if P_const is determined as a value withwhich a desired communication channel capacity can be obtained.

FIG. 4 shows the concept of transmission power control. For example, onthe assumption that the average transmission power is set at 1 under thevariation of the propagation path gain shown in FIG. 1, the result ofcontrolling the transmission power is shown in FIG. 4. In the drawing,the portions surrounded by the thick lines designate signal powers whilethe portions surrounded by the thin lines designate noise powers. Thatis, the transmission powers at the time instants t1, t2, t3 and t4 areset at 11/6, 4/3, 0 and ⅚ respectively. The average transmission poweris expressed by:

( 11/6+ 4/3+0+⅚)/4=1

FIG. 5 shows received power in which the result of the transmissionpower control in FIG. 4 is viewed on the reception side. The receivedpowers at the time instants t1, t2, t3 and t4 are 11/3, 4/3, 0 and 5/9respectively.

FIG. 6 shows a comparative example in which control is made to make thetransmission power proportional to the noise power in order to keep thereceived power or the reception quality constant. That is, thetransmission powers at the time instants t1, t2, t3 and t4 are ⅓, ⅔, 2and 1 respectively. The average transmission power is expressed by:

(⅓+⅔+2+1)/4=1

FIG. 7 is a graph showing an example of a time variation of the receivedpower based on the comparative example of FIG. 6. The received powers atthe time instants t1, t2, t3 and t4, in which the result of powerdistribution (transmission power control) in FIG. 6 is viewed on thereception side, are ⅔, ⅔, ⅔ and ⅔ respectively as shown in FIG. 7.

In FIG. 8, the present invention is compared with the background art asto the control of transmission power relative to a variation of thepropagation path gain. The abscissa designates the propagation pathgain, and the ordinate designates the transmission power as a result oftransmission power control. In the drawing, the outline circlesdesignate the present invention, and the outline diamonds designate thebackground art. That is, the channel gain has a relationship of inverseproportion to the transmission power in the background-art transmissionpower control, in which the transmission power is increased when thechannel gain decreases, and the transmission power is reduced when thechannel gain increases. On the contrary, according to the presentinvention, the transmission power is reduced when the channel gaindecreases, and the transmission power is increased when the channel gainincreases.

In addition, the communication channel capacity attained by thetransmission power control according to the present invention isexpressed by:

C=W(log 2(1+ 11/3)+log 2(1+ 4/3)+log 2(1+0)+log 2(1+ 5/9))/4=1.02W

On the other hand, the communication channel capacity attained by thetransmission power control according to the background art is expressedby:

C=W log 2(1+⅔)=0.737W

Hence, in the examples shown here, the communication channel capacitybased on the power control according to the present invention increasesto be 1.38 (=(1.02/0.737)) times as large as that in the background-artpower control method. On the other hand, in order that the samecommunication channel capacity as the aforementioned communicationchannel capacity in the case where the present invention has beenapplied is attained by use of the background-art transmission powercontrol system, S/N=1.028 is required because 1.02=log 2(1+1.028). Thus,the average transmission power 1.54 (=1.028/(⅔)) times as large as S/N=⅔attained by the aforementioned background-art transmission power controlis required. Accordingly, according to the present invention, thetransmission power for attaining the same communication channel capacityis reduced to 0.649 times as large as that in the case where thebackground art is used.

Description has been made above on the transmission power controlalgorithm for maximizing the communication channel capacitytheoretically. However, substantially equal effect can be obtainedwithout following the aforementioned algorithm strictly. That is,transmission power may be controlled by use of a function approximatingthe relationship between the propagation path gain and the transmissionpower shown in FIG. 8. It is desired that the function has a positiveslope as a whole. For example, substantially equal effect can beobtained even with a simple function by which the transmission power ismade proportional to the propagation path gain.

FIG. 9 is a graph showing a second example of a propagation path gainvariation.

FIGS. 10A to 10D are graphs showing a second embodiment of transmissionpower control according to the present invention.

According to the algorithm for determining the transmission power:

S(t)=P_const−Nr(t)/g(t)

when the propagation path gain increases stepwise at the time instant t0as shown in FIG. 9, the transmission power also varies stepwisecorrespondingly as shown in FIG. 10A. In addition, when there occurs acontrol delay or the like, the transmission power varies with a certainrise time as shown in FIG. 10B.

In the control of FIG. 10A or 10B, the communication channel capacityincreases when a mobile station is located in a place close to a basestation having a high propagation path gain, and on the contrary thecommunication channel capacity decreases when the mobile station islocated in a place distant from the base station. When such a differenceis not preferable on the system design, practically, P_const iscontrolled comparatively slowly by use of the average gain and theaverage noise power in the current communication channel situation, forexample, by:

P_const=C0Ave(Nr(t))/Ave(g(t))

Here, Co designates a constant. Consequently, the aforementioned powercontrol is applied to a short-periodical variation of the communicationchannel while obtaining a substantially constant communication channelcapacity regardless of a distance from the base station.

In this case, response to the aforementioned variation of thepropagation path gain shown in FIG. 9 is made so that transmission poweras shown in FIG. 10C or 10D is similar to the aforementionedtransmission power in FIG. 10A or 10B for a short period of time,whereafter the transmission power approaches gradually to transmissionpower canceling the variation of the propagation path gain in the samemanner as that under the background-art power control.

According to the above power control, the communication channel capacityvaries with time. For this reason, it is therefore preferable that thebit rate is controlled so as to make communication at a high bit ratewhen the reception quality is good and the communication channelcapacity is not lower than its average over a certain period of time,and so as to make communication conversely at a low bit rate when thereception quality is bad and the communication channel capacity is nothigher than the average.

In addition, when the average times Ave(Nr(t)) and Ave(g(t)) used forcalculating P_const are made consistent with the unit with whichcommunication channel coding is executed, the average bit rate can beenhanced without controlling the bit rate explicitly. Thus, this manneris suitable to a system required to have a fixed bit rate.

In the background-art power control, the communication channel capacityis fixed by fixing the reception quality. Thus, the communicationchannel has a characteristic close to AWGN (Additive White GaussianNoise). Therefore, error correction coding suitable for the AWGNcommunication channel is suitable.

On the other hand, in the aforementioned power control, the receptionquality has a large variation so that a part of Received Data is nearlyomitted.

Accordingly, for a variation having a comparatively short period oftime, it is preferable that time correlativity of the variation of thereception quality is eliminated by interleave, and further, powerfulerror correction codes such as turbo codes or the like are applied sothat Received Data poor in reception quality is remedied with ReceivedData good in reception quality by use of the redundancy of the errorcorrection codes.

It is also preferable to apply LDPC (Low Density Parity Check) codes,product codes, or the like, instead of turbo codes.

More generally, it is preferable to apply error correction codes havingdependency in which a large number of bits constituting a code word havebeen catenated complicatedly, and known to have a high error correctioncapacity when iterative decoding is applied to perform decoding againusing a halfway result of decoding.

In addition, the remedy using error correction cannot be attained whenthe bad condition of the reception quality continues over a certainperiod of time (for example, a period of time corresponding to onecoding unit of error correction codes or one interleave unit).

Description will be made below on the system and the apparatusconfiguration for carrying out the aforementioned algorithm.

FIG. 30 shows the system configuration according to the presentinvention. A plurality of mobile stations 3, 4 and 5 make communicationwith base stations 1 and 2 by wireless so that the base stations 1 and 2establish communication of the aforementioned mobile stations with eachother or with communication equipment belonging to a fixed network underthe control of a base station control center 6.

FIG. 11 shows the configuration of a reception-side WirelessCommunication Station according to the present invention.

FIGS. 12A to 12C show format diagrams of first examples of atransmission signal multiplexing format of the transmission-sideWireless Communication Station according to the present invention.

FIG. 13 shows the configuration of a transmission-side WirelessCommunication Station according to the present invention.

FIGS. 14A and 14B show format diagrams of examples of a transmissionsignal multiplexing format of the reception-side Wireless CommunicationStation according to the present invention.

Here, one of Wireless Communication Stations whose transmission powerand data rate are controlled according to the present invention is setas the transmission-side Wireless Communication Station, while the otheris set as the reception-side Wireless Communication Station. On thesystem configuration shown in FIG. 30, there is no preference as towhich station, the mobile station or the base station, is thetransmission-side Wireless Communication Station and which station isthe reception-side Wireless Communication Station. When the base stationis set as the transmission-side Wireless Communication Station,transmission power control and bit rate control are carried out upon adownstream signal. On the contrary, when the mobile station is set asthe transmission-side Wireless Communication Station, transmission powercontrol and bit rate control are carried out upon an upstream signal.

A signal received through an antenna in FIG. 11 is converted into abaseband signal by a Radio Frequency Circuit 101. Demodulationprocessing such as detection and the like is carried out upon thebaseband signal by a demodulator 102, and error correction is carriedout on the demodulated baseband signal for every coding unit by acommunication channel decoder 121.

Incidentally, at the time of decoding in the communication channeldecoder 121, any missing data may be decoded without waiting foraccumulation of all the data corresponding to one coding unit on theassumption that a signal whose power is zero has been received. Thus,decoding can be performed without waiting for accumulation of all thedata corresponding to one coding unit. Decoding is carried out at anytime in the course of accumulating the data corresponding to one codingunit. The result error-corrected by the communication channel decoder121 is supplied to a reception quality judging portion 140, and errorsare detected in an error detecting portion 116. Thus, thepresence/absence of any error is made up as reception qualityinformation. On the other hand, the aforementioned baseband signal issupplied to a power signal generating portion 105 so as to generate atransmission power control signal following the aforementioned powercontrol algorithm. The reception quality information and thetransmission power control signal are multiplexed by a multiplexer 109together with a third pilot signal generated by a third pilot signalgenerating portion 130, and a data signal subjected to communicationchannel encoding in an error correction encoder 106 and an interleaver107. The multiplexed signal has a format in FIG. 14A or 14B by way ofexample. The reference numeral 303 represents the data signal; 304, thepower control signal; 305, the third pilot signal; and 306, thereception quality information signal. In the drawings, the widthwisedirection designates time, and the lengthwise direction designates codesused for code division. Multiplexing is carried out in a multiplexingmethod such as time division multiplexing, code division multiplexing,or the like. The aforementioned multiplexed signal is modulated by amodulator 110, and sent to a wireless propagation path through the RadioFrequency Circuit 101.

The signal sent from the reception-side Wireless Communication Stationis received by the transmission-side Wireless Communication Stationshown in FIG. 13. The operations of members 101, 102, 103 and 104 aresimilar to those in the reception-side Wireless Communication Station. Atransmission power control portion 111 extracts the aforementioned powercontrol signal 304, and calculates transmission power corresponding tothe extracted transmission power control signal 304. A reception qualitysignal extracting portion 141 extracts the aforementioned receptionquality information signal 306, and notifies data rate control means 142of the presence/absence of errors detected by the error detectingportion 116. In the data rate control means 142, transmission dataencoded by a communication channel encoder 122 is accumulated for everycoding unit. Then, the data rate is changed in accordance with theaforementioned information of the presence/absence of errors reported bythe reception quality signal extracting portion 141, while thetransmission data added with data for identifying the coding unit isoutputted to a multiplexing portion 112.

FIG. 31 shows an example of a processing flow carried out by the datarate control means 142. In the flow of processing in FIG. 31, the datarate control means 142 divides the encoded transmission data into aplurality of blocks by coding unit, and transmits a block of thetransmission data. When the data rate control means 142 is notified ofno error, the data rate control means 142 terminates the transmission.When the data rate control means 142 is not notified of no error, thedata rate control means 142 transmits a block following the previouslytransmitted block. When the data rate control means 142 is not notifiedof no error after finishing transmitting all the blocks, the data ratecontrol means 142 repeats transmission from the start block again. Thus,the transmission data outputted from the data rate control means has adata rate necessary and sufficient for meeting the varying communicationchannel capacity. The transmission data outputted from the data ratecontrol means 142 is multiplexed by the multiplexer 112 together with asecond pilot signal generated by second pilot signal generating means108, and supplied to transmission power varying means 113. Thetransmission power varying means 113 varies the signal amplitudecorrespondingly to the transmission power specified by theaforementioned transmission power control portion 111. The output of thetransmission power varying means 113 is multiplexed by a multiplexer 115together with a first pilot signal set to have a predetermined power byfirst pilot signal generating means 114, so that the multiplexed signalis formed into a format shown in anyone of FIGS. 12A to 12C. In FIGS.12A to 12C, the reference numeral 301 represents the first pilot signal;302, the second pilot signal; and 303, the data signal.

As shown in FIGS. 12A to 12C, various multiplexing formats can beadopted. In addition, the first pilot signal 301 (P0) is transmitted bypredetermined power without receiving the aforementioned power controlfrom the transmission power control portion 111. On the other hand,while receiving the aforementioned power control, the second pilotsignal 302 is transmitted together with the data signal 303. The signalmultiplexed in the format shown in any one of FIGS. 12A to 12C ismodulated in a modulator 110 and sent to the wireless propagation paththrough the Radio Frequency Circuit 101.

FIG. 15 shows a block diagram of a first configuration example of atransmission power control signal generating portion according to thepresent invention.

FIG. 16 shows a block diagram of a first configuration example of atransmission power control portion according to the present invention.

For example, the aforementioned transmission power signal generatingportion 105 in the reception-side Wireless Communication Station and theaforementioned transmission power generating portion 111 in thetransmission-side Wireless Communication Station are configured as shownin FIGS. 15 and 16, respectively. The transmission power signalgenerating portion in FIG. 15 separates the first pilot signal and thesecond pilot signal in first pilot signal separating means 201 andsecond pilot signal separating means 205 respectively. The transmissionpower signal generating portion uses a comparator 211 to judge whethercurrent transmission power is larger or smaller than the transmissionpower satisfying:

P_const=C0Ave(Nr(t))/Ave(g(t))

when:

S(t)=P_const−Nr(t)/g(t)

Then, the transmission power signal generating portion generates atransmission power control signal 304 giving an instruction to reducethe transmission power when the current transmission power is larger,and an instruction to increase the transmission power when the currenttransmission power is smaller. Accordingly, the transmission powercontrol portion in FIG. 16 extracts the aforementioned transmissionpower control signal 304, and increases/reduces the current transmissionpower in accordance with the transmission power control signal.Incidentally, although noise power is obtained from the second pilotsignal in FIG. 15, it may be obtained from the first pilot signal(broken line).

FIG. 32 shows a block diagram of a configuration example of an errorcorrection encoder 106.

In FIG. 32, encoding is performed with turbo codes. Input transmissiondata is encoded in accordance with data rate information, and anencoding result is outputted.

The input transmission data is convolutionally encoded by a recursiveconvolutional encoder E1 (231) so as to be formed into a signal Y1.

In addition, the data order of the aforementioned transmission data ischanged by an interleaver 230. Then, the transmission data isconvolutionally encoded by another recursive convolutional encoder E2(232) so as to be formed into a signal Y2.

After that, original transmission data X (or U) and the signals Y1 andY2 are integrated into one signal by a parallel-to-serial (P/S)converter 233, and an encoding result is outputted.

FIG. 33 shows a block diagram of a configuration example of an errorcorrection decoder 104.

FIG. 33 shows an error correction decoder supporting signals encoded bythe turbo encoder in FIG. 32. The error correction decoder carries outerror correction decoding by iterative decoding in accordance with thereception signal information and the data rate information so as tooutput a decoding result U″.

An input reception signal is separated into U′, Y1′ and Y2′ in aserial-to-parallel (S/P) converter 234 by its operation reverse to thatof the aforementioned parallel-to-serial (P/S) converter 233.

A soft decision decoder D1 (235) performs soft decision decodingprocessing corresponding to the aforementioned recursive convolutionalencoder E1 (231) by use of the separated U′ and Y1′.

A decoding result by the soft decision decoder D1 (235) is supplied to asoft decision decoder D2 (238) through an interleaver 237.

On the other hand, the data order of the output U′ of the aforementionedserial-to-parallel (S/P) converter 234 is changed by an interleaver 236,and the transposed data is supplied to the aforementioned soft decisiondecoder D2 (238).

Here, the interleavers 236 and 237 follow the same order change rule asthat of the interleaver 230 in FIG. 32.

The soft decision decoder D2 (238) carries out soft decision decodingusing the output Y2′ of the aforementioned serial-to-parallel (S/P)converter 234, the output of the aforementioned interleaver 236, and theoutput of the aforementioned interleaver 237, so that a decoding resultis outputted.

The decoding result of the soft decision decoder D2 (238) is supplied toa deinterleaver 239 so as to be transposed in data order.

The deinterleaver 239 operates to restore the data order by theoperation reverse to those of the aforementioned interleavers 230, 236and 237.

The output of the deinterleaver 239 is supplied to the aforementionedsoft decision decoder D1 (235) so as to be subjected to decodingprocessing again.

In such a manner, the reception signal is passed through the softdecision decoders D1 (235) and D2 (238) repeatedly and alternately.Thus, precision of decoding is enhanced.

After decoding is performed a sufficient number of times, one of thedecoding results of the soft decision decoders D1 (235) and D2 (238) isoutputted as a final decoding result.

Although FIGS. 32 and 33 show an example using turbo codes, as describedpreviously, the error correction encoder and the error correctiondecoder may support error correction codes such as LDPC codes, productcodes, or the like, capable of exhibiting high error correction capacityby iterative decoding processing.

FIG. 17 is a block diagram of a second configuration example of anencoder with a data rate control function according to the presentinvention.

FIG. 18 is a block diagram of a second configuration example of adecoder with a data rate control function according to the presentinvention.

In the above embodiment, as described previously, it is preferable thatthe bit rate is controlled so as to make communication at a high bitrate on average when the communication channel capacity is not lowerthan the average over a certain period of time, and so as to makecommunication conversely at a low bit rate on average when thecommunication channel capacity is not higher than the average. To thisend, it will go well if a communication channel encoder and acommunication channel decoder as shown in FIGS. 17 and 18 respectivelyare used in place of the communication channel encoder 122 in FIG. 13and the communication channel decoder 121 in FIG. 11. The communicationchannel encoder shown in FIG. 17 includes: an error correction encoder106 for carrying out encoding at a data rate specified by a data rateinstruction; a rate information generating portion 123 for generatingdata rate information, which is information about the data ratespecified by the data rate instruction, and outputting the data rateinformation; an interleave portion 107 for carrying out interleaveprocessing upon the output of the error correction encoder 106; and amultiplexing portion 124 for multiplexing the output of the interleaveportion 107 and the output of the rate information generating portion123.

On the other hand, the communication channel decoder shown in FIG. 18includes a rate information separating portion 125 for separating thedata rate information from a received signal, a deinterleave portion 103for deinterleaving the rest data from which the data rate informationhas been separated, and an error correction decoder 104 for decoding theoutput of the deinterleave portion in accordance with the separated datarate information.

FIG. 19 shows an example of the configuration of the aforementionedtransmission power control portion 105. In the drawing, a functionoperating portion 214 operates a function f(x) whose output increases asan input signal increases. Consequently, when the propagation path gainincreases beyond its average value, a transmission power control signalgiving an instruction to increase the transmission power is generated.

FIG. 20 shows an example of the configuration simplified in the case towhere it can be granted that noise power is constant regardless of time.

FIGS. 21A and 21B, FIGS. 22 to 25, FIGS. 26A and 26B, and FIGS. 27 to 29are diagrams showing other modified examples of the present invention.

Also when the second pilot signal 302 is not included in a signal to betransmitted by the transmission-side Wireless Communication Station asis shown in FIGS. 21A and 21B, for example, standardized transmissionpower S(t)/P0 may be obtained by the configuration shown in FIG. 22 sothat, by use of this standardized transmission power S(t)/P0 as atransmission power control signal, S(t) can be obtained by thetransmission power control portion shown in FIG. 23. More simply, theconfiguration of FIG. 24 and the configuration of FIG. 25 may be used inplace of the configuration of FIG. 22 and the configuration of FIG. 23respectively.

In addition, also when the first pilot signal 301 is not included in asignal transmitted by the transmission-side Wireless CommunicationStation as shown in FIGS. 26A and 26B, for example, S(t) can be obtainedby the transmission power control signal generating portion shown inFIG. 27 and the transmission power control portion shown in FIG. 16.More simply, the configuration of FIG. 28 and the configuration of FIG.29 may be used in place of the configuration of FIG. 27 and theconfiguration of FIG. 16 respectively.

According to the embodiments of the present invention described above,it is possible to provide a transmission power control method whichattains a desired reception quality while preventing increase in theaverage transmission power even when there occurs a propagation pathgain variation having a comparatively short period of time. In addition,it is possible to keep the communication channel capacity large evenwhen there occurs a propagation path gain variation having acomparatively short period of time.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A communication control method for transmission control in a wirelesscommunication system, comprising: a first step for controlling data rateof a transmission signal including a step for generating a coding unitencoded with transmission data and transmitting the coding unit, andincluding a step for judging whether or not to continue to transmit thecoding unit at any time of transmitting a part or all of a coding unitthereby to control a data rate of transmitting in response to apresence/absence of error for the coding unit; and a second step forcontrolling transmission power of a signal transmitted from saidtransmitter to said receiver in response to a quality of propagationpath between a receiver and a transmitter.
 2. A communication controlmethod according to claim 1, wherein said third step includes a step fordecreasing transmission power when the quality of the propagation pathis a first quality and increasing transmission power when the quality ofthe propagation path is a second quality better than the first quality.